This invention relates to a drive force transmission in a hybrid vehicle.
Tokkai Hei 11-241624 published by the Japanese Patent Office in 1999 discloses a hybrid vehicle which combines an electric motor with an engine as a source of drive force.
A first electric motor in this hybrid vehicle is directly connected to an input shaft of an automatic transmission. An engine is also connected to the input shaft through a clutch. The vehicle starts moving by using only the motive force of the first electric motor while the clutch is disengaged.
After the vehicle has started, the engine is started by a second electric motor. While the vehicle is running, the engine drives the second electric motor as a generator to charge a battery. When the load on the first electric motor increases during acceleration, the clutch is engaged, and the motive force of the engine is input to the automatic transmission. The motive force of the engine increases the drive force of the vehicle by assisting the motive force of the first electric motor.
The first electric motor and engine of the hybrid vehicle are directly connected when the clutch is engaged and the first electric motor rotates at the same speed as the engine.
It is often the case that high-load conditions including vehicle acceleration coincide with low engine rotation speeds, However, operational efficiency of the electric motor is low in low rotation speed regions.
In other words, it is difficult to obtain a preferred operational efficiency of the engine and of motor at the same time when the vehicle is running on both the engine and motor.
Of course, an electric motor of a larger output can be used in order to increase the vehicle drive force, but such a motor generally has larger volume and weight.
Furthermore in this hybrid vehicle, it is indispensable to provide a forward/reverse change-over mechanism between the first electric motor and the automatic transmission so as to allow the forward and reverse motions of the vehicle.
It is therefore an object of this invention to improve the energy efficiency of a hybrid vehicle.
It is a further object of this invention to downsize the electric motor while maintaining the generated torque of the electric motor.
It is yet a further object of this invention to simplify the structure of a forward/reverse change-over mechanism.
In order to achieve the above objects, this invention provides a drive force transmission mechanism for such a hybrid vehicle that comprises an engine and a motor/generator as a motive force source. The mechanism comprises a first clutch connected to the engine, the first clutch comprising an output shaft that rotates together with the engine when the first clutch is engaged;
a planetary gear set connecting the motor/generator to the output shaft;
an automatic transmission comprising an input shaft, the hybrid vehicle running in accordance with an output rotation of the automatic transmission; and a second clutch selectively connecting the input shaft to the motor/generator and to the output shaft.
The details as well as other features and advantages of this invention are set forth in the remainder of the specification and are shown in the accompanying drawings.